Tubing anchor

ABSTRACT

A tubing anchor for anchoring the lower extremity of a string of oil well tubing to a well casing. The anchor includes a hollow cage formed with a longitudinal passage having transversely opening windows formed therein. Sliders are disposed in the windows are slidable from a retracted position in said windows to an extended position projecting from said windows for engagement with the surrounding casing. A flexible boot lines the interior wall of the passage and is adhered to the interior wall of the passage and also to the back surfaces of the sliders. The boot has sufficient stiffness to normally maintain the sliders retracted within the windows and has sufficient flexibility to enable the pressure buildup within such boot as a consequence of a predetermined head of liquid in the tubing to flex such boot outwardly in the area of such windows to move the sliders to their extended position for engagement with the casing surrounding the tubing to maintain the tubing anchored firmly with respect thereto.

United States Patent Primary Examiner-James A. Leppink Att0rney-Fulwider, Patton, Rieber, Lee & Utecht ABSTRACT: A tubing anchor for anchoring the lower extremity of a string of oil well tubing to a well casing. The anchor includes a hollow cage formed with a longitudinal passage having transversely opening windows formed therein. Sliders are disposed in the windows are slidable from a retracted position in said windows to an extended position projecting from said windows for engagement with the surrounding casing. A flexible boot lines the interior wall of the passage and is adhered to the interior wall of the passage and also to the back surfaces of the sliders. The boot has sufficient stiffness to normally maintain the 'sliders retracted within the windows and has sufficient flexibility to enable the pressure buildup within such boot as a consequence of a predetermined head of liquid in the tubing to flex such boot outwardly in the area of such windows to move the sliders to their extended position for engagement with the casing surrounding the tubing to maintain the tubing anchored firmly with respect thereto.

TUBING ANCHOR BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anchor for anchoring the lower extremity of a string of tubing to a casing into which such tubing is projected.

2. Description of the Prior Art Anchoring devices have been proposed which include sliders positioned within windows formed in a cage and extendible to extended positions under the influence of hydrostatic pressure resulting from the head of fluid within the anchor to thereby maintain the sliders frictionally engaged with the surrounding casing. However, separate retaining means and/or biasing means are normally required for retaining the sliders in the windows and maintaining them retracting to their retracted position to clear the surrounding casing. Anchoring devices of this type are shown in US. Pat. Nos. 2,603,163, 2,670,181, 3,318,385, 2,785,758 and 3,080,924. There are no tubing anchors known to applicant which incorporate flexible boots lining the interior of the cage and bonded thereto and also bonded to the sliders and having sufficient stiffness to normally maintain the sliders retracted while hav ing sufl'icient flexibility to enable the pressure head built up in the tubing to flex the boot outwardly and extend such sliders to their extended position for frictional engagement with the surrounding casing.

SUMMARY OF THE INVENTION The tubing anchor of present invention is characterized by a cage formed with a longitudinal passage having transversely extending through passages which define windows for receipt of closely fitting sliders. A flexible boot lines the interior of the caging and is bonded thereto and is also bonded to the back side of the sliders and has sufficient stiffness to normally maintain the sliders in a retracted position and disengaged from the surrounding casing. The boot has sufficient flexibility to enable the pressure head normally built up in the anchor to flex such boot outwardly to move the sliders into frictional engagement with the surrounding casing to hold the anchor firmly against movement with respect thereto.

An object of the present invention is to provide a tubing anchor of the type described wherein the boot is bonded directly to the interior surface of the cage to form a seal to prevent leakage out the windows.

Another object of the present invention is to provide a tubing anchor of the type described wherein the flexible boot serves as a biasing member to normally maintain the sliders in their retracted position.

Still another object of the present invention is to provide a tubing anchor of the type described which is relatively inex pensive to manufacture and does not require auxiliary seals at opposite ends of the boot.

These and other objects and the advantages of the present invention will become apparent from a consideration of the following detailed description when taken in conjunction with the accompanying drawing.

DESCRIPTION OF THE DRAWING FIG. 1 is a vertical sectional view through an oil well casing showing a side elevational view of a tubing anchor embodying the present invention;

FIG. 2 is a horizontal sectional view taken along the line 2- 2 of FIG. 1;

FIG. 3 is a vertical sectional view taken along the line 3-3 of FIG. 2; and

FIG. 4 is a horizontal sectional view taken along the line 41-4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 3 and 4, the tubing anchor, generally designated 11, of present invention is intended for anchoring the bottom extremity of a string of tubing 13 to a surrounding casing 15. The anchor 11 includes a hollow cage, generally designated 17, formed with a through vertical passage 19 having a plurality of radially extending windows 23 therein. Slidably received in the windows 23 are respective sliders 27 which are shiftable from the retracted broken line position shown in FIGS. 3 and 4 to the extended solid line position frictionally engaging the interior of the casing 15. The interior of the cage 17 is lined with a heavy walled flexible boot 31 which is bonded to the interior of the casing and is also bonded to the back side of the sliders 27 The boot 31 has sufficient stiffness to normally retain its unflexed configuration shown in solid lines in FIG. 3 to retain the sliders 27 in their respective retracted positions. When the anchor 11 is lowered into the lower extremity of the casing 15 and a head of oil or the like builds up therein, the boot 31 will be flexed to project the sliders 27 to their projected position as shown in solid lines in FIGS. 3 and 4, to frictionally engage the walls of the casing 15 to secure such anchor firmly to said casing.

Still referring to FIG. 3, the cage 17 is formed on its upper end with female threads 35 for engagement with male threads formed on the lower extremity of tubing 13. The lower extremity of the cage 17 is formed with female threads 39 for en gagement with male threads formed on the upper extremity of an oil well pump 41.

The windows 23 are generally oblong in their vertical direction and are arranged in upper and lower rows extending peripherally around the cage 17 to thereby provide a relatively large amount of total window area while maintaining the total area of each window relatively small to maintain the wall of the cage 17 relatively strong for withstanding the high pressures experienced therein during pumping of an oil well without being overstressed and bulging. The sliders 27 are formed to closely fit the windows 23 to prevent the high pressures in the passage 19 from extruding the boot 31 outwardly through the cracks formed between the respective sliders 27 and windows 23.

The vertical passage 19 has an enlarged longitudinal cylindrical bore 45 cut therein for a length extending from above to below the windows 23 for receipt of the boot 31, the opposite ends of such enlarged bore defining shoulders against which the opposite ends of the abut. The boot 31 has its outer periphery bonded directly to the interior of the cage 17 and also to the back sides 49 of the respective sliders 27. A particularly convenient way for forming the boot 31 is to form the cage 17 with the windows 23 therein and position the sliders 27 within such windows. The interior of the cage and back surface 49 of the sliders 27 are thoroughly cleaned and a bonding agent painted thereon. A plunger defining the passage 19 is then projected through the interior of the cage 17 and rubber is molded around such plunger to form the boot 31.

In operation, an oil well pump 41. is secured to the lower extremity of the anchor 11 by means of the threads 39. The anchor 11 itself is then secured to the lower extremity tubing string 13 by means of the threads 35. Thereafter, the pump 41 and anchor 11 are lowered into the casing 15, the boot 31 serving to maintain the sliders 27 retracted to their broken line position shown in FIG. 3 thereby maintaining them disengaged from the wall of the casing 15. Thereafter, a string of sucker rods 51 may be inserted within the tubing 13 for engagement with the plunger of the pump 41.

As the pump 41 is actuated, the pressure within the passage 19 will build up as a consequence of the head of oil pumped upwardly through the interior of the tubing 13. Such head of oil will act to flex the boot 31 outwardly in the area of the windows 23 to thereby move the sliders 27 to their extended position for engagement with the wall of the casing 15. The pressure within the cage 17 may build up to 3000 p.s.i. thereby resulting in firm engagement of the sliders 27 with the casing to assure firm anchoring of the anchor 11 to the casing to securely anchor the tubing 13 to avoid shock to the pump 41. By merely dissipating the head of oil in the tubing IS, the pressure within the boot 31 will be reduced to enable such boot to retract the sliders 27 to disengage them from the casing 15 to enable free removal of the anchor and avoiding freezcup between such anchor and the casing which may result in breaking of the tubing string 13 along its length.

it is of importance that the outer surface of the respective sliders 27 is relatively smooth to thereby avoid gouging the interior surface of the casing 15 and avoiding positively anchoring the anchor 11 to the casing to thereby enable such anchor to give a limited amount upon application of erratic forces to provide for some shock absorption to avoid breakage.

Various modifications and changes may be made with regard to the foregoing without departing from the spirit of the invention.

1 claim:

1. A tubing anchor for anchoring the lower extremity of a string of well tubing to the well casing, said anchor comprismg:

a hollow cage for receipt in said casing and formed with a longitudinal passage having a plurality of transversely opening, through windows formed in the wall thereof;

sliders formed to closely fit said windows and slidably received in the respective windows for movement from a retracted position disengaged from the wall of said casing to an extended position projecting from said windows and frictionally engaged with said casing wall;

a flexible hoot lining the wall of said passage; and bonding means bonding said boot to the wall of said cage and to said sliders, said boot being characterized in that it has sufficient stiffness to normally maintain an unflexed configuration behind said sliders to maintain said sliders in said retracted position disengaged from said wall of said casing and having sufficient flexibility to enable a predetermined pressure within said passage to flex said boot outwardly behind sliders to shift said sliders to their extended position whereby said boot will maintain said sliders retracted while said anchor is inserted in said casing and when fluid pressure builds up in said passage said boot will seal the fluid from passage through said windows and when the pressure in said boot reaches said predetermined pressure said boot will flex outwardly behind said sliders to move said sliders to said extended position for frictional engagement with said casing to anchor said tubing securely to said casing.

2. A tubing anchor as set forth in claim 1 wherein: said windows are arranged in at least two rows spaced vertically from one another whereby each individual window may be relatively small while the cumulative area thereof will be relatively large.

3. A tubing anchor as set forth in claim 1 wherein: said sliders are formed with relatively smooth exterior surfaces for engagement with said casing. 

1. A tubing anchor for anchoring the lower extremity of a string of well tubing to the well casing, said anchor comprising: a hollow cage for receipt in said casing and formed with a longitudinal passage having a plurality of transversely opening, through windows formed in the wall thereof; sliders formed to closely fit said windows and slidably received in the respective windows for movement from a retracted position disengaged from the wall of said casing to an extended position projecting from said windows and frictionally engaged with said casing wall; a flexible boot lining the wall of said passage; and bonding means bonding said boot to the wall of said cage and to said sliders, said boot being characterized in that it has sufficient stiffness to normally maintain an unflexed configuration behind said sliders to maintain said sliders in said retracted position disengaged from said wall of said casing and having sufficient flexibility to enable a predetermined pressure within said passage to flex said boot outwardly behind sliders to shift said sliders to their extended position whereby said boot will maintain said sliders retracted while said anchor is inserted in said casing and when fluid pressure builds up in said passage said boot will seal the fluid from passage through said windows and when the pressure in said boot reaches said predetermined pressure said boot will flex outwardly behind said sliders to move said sliders to said extended position for frictional engagement with said casing to anchor said tubing securely to said casing.
 2. A tubing anchor as set forth in claim 1 wherein: said windows are arranged in at least two rows spaced vertically from one another whereby each individual window may be relatively small while the cumulative area thereof will be relatively large.
 3. A tubing Anchor as set forth in claim 1 wherein: said sliders are formed with relatively smooth exterior surfaces for engagement with said casing. 